Inorganic insulation for electrical sheets



Patented Nov. 27, 1934 1,982,179 INORGANIC INSULATION FOR ELECTRICALSHEETS Charles A. Scharschu, Brackenridge, Pa., assignor to AlleghenySteel Company, a corporation of Pennsylvania No Drawing. ApplicationJune 8, 1931, Serial No. 543,003

3 Claims. (01. 15443) This invention relates to inorganic enamels forelectrical sheets and to a method of applying the same to such sheets.

Hitherto organic enamels or varnishes have been used to coat electricalsheets for the purpose of insulating one sheet from another inelectrical apparatus, thus cutting down the eddy loss. There are,however, many applications for which this type of coating isobjectionable, such as in those cases where it is desired to anneal thepunching after the enamel has been applied.

For producing porcelainic enamels, silicates are generally used, butthese enamels, on account of the properties desired, are more complexthan is preferred in an enamel for electrical sheets and these enamelsare, moreover, of such a composition and fired at such temperatures asto cause the enamel to melt and flow. Enamels of this natureconsequently are not suitable for electrical sheets as such enamelswould cause the individual sheets to stick together when annealed instacks. Again, these enamels are much heavier and more continuous thanis necessary for the insulation of electrical sheets.-

Inorganic enamels when properly made and applied have excellentelectrical resistance and. may be used to coat electrical sheets. Wheninorganic enamels are used the electrical sheet may be enameled beforeit is punched or cut into parts for electrical apparatus and thesepunchings may be subsequently annealed to produce better electricalqualities without destroying the enamel.

One of the objects of this invention is the provision of an inorganicinsulation which will adhere to electrical sheets and which can beuniformly deposited thereupon.

Another object is to provide an inorganic insulation which can besubjected to an anneal without detriment to the enamel.

A further object is the production of an inorganic enamel of certaincomposition which not only has the desired electrical properties butwhich acts as a protective coating for the sheets to prevent rusting ofthe same.

A still further object is the provision of a meth- -od of applying aninorganic insulating material so as to produce an even adherent coatinghaving the desired characteristics.

Other and further objects and advantages will be understood by thoseskilled in this art or will be pointed out hereinafter.

I have found that very simple enamelsare satisfactory for coatingelectrical sheets. For instance, water glass may be used as the sourceof 59 silicate although finely ground silica may also be used. To eitherof these there is added lime and another metallic oxide such as ironoxide, the proportions depending upon the properties desired in theenamel.

For example, these three constituents are used in the followingproportions for certain applications:---

Water 200 cc.

Lime 15 grams Iron oxide 28 grams Water glass '70 grams It is understoodthat magnesium oxide may be substituted for the lime or both may be usedand that silica, preferably in a finely ground condition, may besubstituted for the water glass and the iron oxide may or may not beused depending upon the properties desired in the enamel.

The sheets of material destined for electrical uses are passed singlythrough a bath of the liquid enamel, then through a set of rolls andthrough a drying oven to drive off the water. The rolls cause an evendistribution of the liquid enamel on the surfaces of the sheets andremove excess enamel and may be of any suitable type. If desired, orfound necessary glue or. an excess of water glass'may be added to thebath to make the enamel adhere more tightly to the sheet before thesheets are heated.

The drying oven is kept at a suitable temperature, for example, about600 Fahrenheit, and the coated sheets are passed therethrough at asuitable rate such that the coating is subjected to the heat for abouttwo minutes. The coating is iinally baked on in the anneal which iscarried out at about 1450 Fahrenheit. The temperature of the drying ovenmay vary considerably but in such cases the time of exposure thereto issuitably varied in inverse relationship thereto; that is, the hotter theoven the less the time of exposure and the cooler the oven the greaterthe time of exposure.

I may vary the constituents over wide limits to produce enamels havingdifferent properties, which when baked at the proper temperature form aninsulating enamel suitable for electrical sheets. This enamel,especially when applied to pickled sheets, also acts as a protectivecoating preventing the sheets from rusting.

What I claim as new and desire to secure by Letters Patent is:

1. Steel elements for electrical apparatus coated with an inorganicelectrical insulating enamel consisting substantially entirely of aninsoluble complex silicate unaffected by conditions encountered inannealing such sheets according to commercial practice.

2. Steel elements for electrical apparatus coated with an inorganicelectrical insulation consisting chiefly of silica, iron oxide and anoxide of the alkaline earth metals converted by heat, prior to annealingthe elements, into a complex silicate which is un'afiected by moistureand by conditions of annealing encountered in the processing of suchelements.

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